1. Field for Industrial Utilization
The present invention relates to a roller bearing wherein two members are placed in a relatively infinite rectilinear motion by endlessly circulating in a direction of rectilinear motion, cylindrical rollers or long cylindrical rollers inserted between two members. More specifically, this invention relates to a roller bearing for an infinite rectilinear motion of what is called a parallel-roller type, wherein cylindrical rollers are so arranged that each axis of the rollers are parallel with each other, and directed in the same direction on the truck face of a row in which the cylindrical rollers roll over.
2. Prior Arts
As types of roller-arrangement of this kind of roller bearings for an infinite rectilinear motion on a truck face, there can be classified into a cross-roller type where rollers are so arranged that axes of adjacent rollers may cross perpendicularly with each other, and a parallel-roller type where axes of adjacent rollers are arranged in the same direction.
In the case of a cross-roller type bearing, two rows for endless circulation (endless circulation passage) of rollers are sufficient for the bearing to carry load in every direction, hence it is possible to manufacture a roller bearing of a low sectional height.
But in the case of a parallel-roller type bearing, at least four rows of endless circulation passages for rollers are required for the bearing to carry load in every direction. And as compared with a cross-roller type bearing, the sectional height of the bearing will become greater by the increased number of the row, and its construction will become more complicated.
With reference to FIG. 9, detailed description will be given of a parallel-roller type bearing. FIG. 9 is symmetrical with the center line, so symbols are given only to members on the left side. When a slide unit 11 is mounted astride a truck rail 12, rollers 13 and 13A are inclined, for example, at an angle of 45 degrees, relative to the center line, and are arranged such that each extension line (not illustraed) of the axes (rotation axes) of the rollers 13 and 13A may cross perpendicularly, so that the bearing may carry load in every direction. In a casing 11, return passages 14 and 14A are provided, and the return passages 14 and 14A are connected respectively, through direction change passages 15 and 15A, with two truck grooves in which the rollers 13 and 13A are present.
In order to enable the rollers to smoothly roll over in the truck grooves, direction change passages 15 and 15A, and the return passages 14 and 14A, the return passages 14 and 14A need to be formed respectively at the positions inclined at 45 degrees from the two truck grooves relative to the horizontal plane. A height h1 of the casing 11 to satisfy such conditions tends to become considerably great as compared with that of a cross-roller type bearing. That is, in the conventional parallel-roller type bearing, due to motional characteristics of rollers, a width and a sectional height will inevitably become great (for example, refer to Japanese Patent Application No. 248789-1983 etc.), further the number of parts tend to by many, and the bearing becomes expensive.
To reduce the casing height, a proposal was made that the truck grooves, direction change passages 15 and 15A, and return passages 14 and 14A are cross arranged in such a relation as shown in FIG. 10, (for example, refer to Japanese Patent Application No. 94552-1981). In this case, the height h2 of the casing 11 is fairly smaller than in the case of FIG. 9 (height h1). However, it requires very complicated and difficult machining processes to work and form the inside of the casing 11 such that the direction change passage 15 and 15A may cross without interfering each other, and therefore, further accurate manufacture of the bearing is difficult, and that leads to increase of manufacturing cost.